NEST-SITE PREFERENCE OF NORTHERN GOSHAWKS IN SOUTH-CENTRAL WYOMING

In 1992, we studied the nest-site preference of goshawks (Accipiter ge ntilis atricapillus) nesting in lodgepole pine (Pinus contorta) forest s of the Medicine Bow National Forest, southcentral Wyoming. For 39 ac tive pairs of goshawks, we described nesting habitat at 3 spatial scal es: nest tree, nest-tree area (0.04 ha circle centered at nest tree), and nest stand (homogeneous forest stand surrounding nest). Nest stand s ranged from 0.4 ha to 13.0 ha ((x) over bar = 2.7 ha, SE = 0.4). We compared habitat characteristics at nest-sites to those measured at ra ndom sites. The mean diameter at breast height (dbh) of nest trees was larger (P < 0.001) than the mean dbh of trees in either the nest-tree area or the nest stand. Nest trees also were taller (P < 0.001) and h ad greater dbh (P < 0.001) than trees in random stands. Slopes at gosh awk nests were more (P = 0.04) moderate ((x) over bar = 11%, SE 1.1, r ange 1 to 34%) compared to those available. Aspects at goshawk nests w ere similar (P = 0.61) to those available. The tree density in goshawk nest stands was lower (P = 0.045) than random stands: However, nest s tands had a higher (P < 0.001) density of large trees compared to rand om stands. Trees in nest stands also were taller (P < 0.001) with grea ter (P = 0.006) heights to live canopy compared to trees in random sta nds. The mean density of small trees at nest stands was less than (P = 0.001) one-half those present in random stands. Nest stands were not old-growth in the classic sense of being multi-storied stands with lar ge diameter trees, high canopy closure, and abundant woody debris. Rat her, nest stands were in even-aged, single-storied, mature forest stan ds with high canopy closure ((x) over bar = 65%, SE 1.4) and clear for est floors. We recommend changes in procedures for identifying mature and old-growth lodgepole pine forests and describe silvicultural metho ds for creating goshawk nest stands.